On Tue, Feb 11, 2020 at 09:15:02AM +0100, Geert Uytterhoeven wrote: > Hi Greg, > > CC man > > On Mon, Feb 10, 2020 at 9:57 PM Greg Kroah-Hartman > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Jan 30, 2020 at 01:32:50PM +0100, Geert Uytterhoeven wrote: > > > On Wed, Jan 29, 2020 at 5:20 PM Eugeniu Rosca <erosca@xxxxxxxxxxxxxx> wrote: > > > > From: Torii Kenichi <torii.ken1@xxxxxxxxxxxxxx> > > > > > > > > This patch is necessary to use BT module and XM module with DENSO TEN > > > > development board. > > > > > > > > This patch supports ASYNC_SPD_CUST flag by ioctl(TIOCSSERIAL), enables > > > > custom speed setting with setserial(1). > > > > > > > > The custom speed is calculated from uartclk and custom_divisor. > > > > If custom_divisor is zero, custom speed setting is invalid. > > > > > > > > Signed-off-by: Torii Kenichi <torii.ken1@xxxxxxxxxxxxxx> > > > > [erosca: rebase against v5.5] > > > > Signed-off-by: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx> > > > > > > Thanks for your patch! > > > > > > While this seems to work fine[*], I have a few comments/questions: > > > 1. This feature seems to be deprecated: > > > > > > sh-sci e6e68000.serial: setserial sets custom speed on > > > ttySC1. This is deprecated. > > > > > > 2. As the wanted speed is specified as a divider, the resulting speed > > > may be off, cfr. the example for 57600 below. > > > Note that the SCIF device has multiple clock inputs, and can do > > > 57600 perfectly if the right crystal has been fitted. > > > > > > 3. What to do with "[PATCH/RFC] serial: sh-sci: Update uartclk based > > > on selected clock" (https://patchwork.kernel.org/patch/11103703/)? > > > Combined with this, things become pretty complicated and > > > unpredictable, as uartclk now always reflect the frequency of the > > > last used base clock, which was the optimal one for the previously > > > used speed.... > > > > > > I think it would be easier if we just had an API to specify a raw speed. > > > Perhaps that already exists? > > > > Yes, see: > > http://www.panix.com/~grante/arbitrary-baud.c > > Thanks a lot!! > This must be one of the most guarded secrets of serial port programming ;-) It really is, I have to look it up each time it comes up :( > Implemented since 2006, commit edc6afc5496875a6 ("[PATCH] tty: switch to > ktermios and new framework"), not documented in today's man-pages. yeah, serial port control really needs to be documented better, there's all sorts of nice ways of controlling them that people don't seem to know about. I used to have a link to a bunch of online examples, but can't seem to find that anymore either. Ugh, another thing for the long TODO file... greg k-h
